PHILADELPHIA — In his team’s tiny locker room beneath the Lincoln Financial Field stands, Washington Redskins Coach Jay Gruden looked hard at his players late Monday night and said the only thing that he possibly could on an evening when their playoff hopes may well have died.

“We can’t feel sorry for ourselves,” he said.

They had lost for the third straight time, a 28-13 defeat to the Philadelphia Eagles, made much, much worse by the fact they had just lost their second quarterback to a broken leg in the past three games. Now, at 6-6, tied for second in the NFC East with the Eagles and a game behind the division-leading Dallas Cowboys, the players who looked back at Gruden realized they somehow would have to fight for the postseason with a quarterback, Mark Sanchez, who admitted he doesn’t know many of their names.

Given they are looking from the outside at the playoffs and that before Monday, Sanchez hadn’t played in an NFL game for more than a year, any playoff dreams would seem preposterous — especially considering they had also lost their third starting guard, Jonathan Cooper, for the season with a torn muscle in his arm, and their defense had given up 436 yards to an Eagles team that has struggled on offense for most of the year.

“Our backs are against the wall, man. We’re going to see what we are made of the next few weeks,” running back Adrian Peterson said.

“Now it goes from contingency plan to game plan,” Sanchez said. “There’s no excuses, and — to be honest — nobody cares.”

Perhaps to speak to the sudden fragility of this team, Sanchez was speaking to the media for the first time as a member of the Redskins. From the minute he had been signed, two weeks ago Monday, every spare moment had been spent cramming for an emergency nobody really imagined. But, thrust into the game early in the second quarter, he did what Gruden called “a pretty good job there for a while.” Sanchez finished 13 for 21 for 100 yards with no touchdowns and an interception.

Adding to the insanity of a night that was almost beyond description, Peterson took a handoff on Sanchez’s first snap and ran 90 yards for a touchdown that was not only the longest run of his career but the longest in Redskins history. And yet none of it would be enough, mainly because Sanchez was basically playing with a tiny handful of plays hastily given to him just in case something bad happened to McCoy — and because a once-stout defense was again soft, giving up more than 400 yards for the fourth time in five games.

“You have to adjust, and we didn’t do a good enough job of adjusting tonight,” Gruden said in reference to the defense’s lapses.

Later, he was stronger in his criticism of the defense, saying, “The [436] yards was too much for the defensive personnel we have.”

The more immediate problem was replacing McCoy. He broke his leg just before the end of the first quarter when he slipped on the turf with Washington down 7-0 and banged his lower right leg into the knee of Philadelphia’s Malcolm Jenkins. He managed to stay in for two more plays, even completing a pass that set up a field goal early in the second quarter.

Still, it was clear he was severely injured. He hobbled off the field and appeared unable to walk. He wobbled toward the locker room, supported by two trainers, inching slowly through the tunnel.

A few minutes later, Sanchez stepped onto the field in what appeared to be dire circumstances. He hadn’t played in an NFL game since Jan. 1, 2017, as a member of the Cowboys, but all he had to do on his first play was hand the ball to Peterson, who tore off on his touchdown run. In all the mayhem, the Redskins ­actually had the lead at 10-7.

Late in the half, Philadelphia came back, taking a 14-10 lead on Darren Sproles’s 14-yard touchdown run. The drive took just three plays, aided by a roughing-the-passer penalty against cornerback Greg Stroman.

Perhaps improbably, Sanchez marched the Redskins’ offense down the field in less than two minutes after the Redskins took over at their 25-yard line. He completed five straight passes around a sack to move Washington to the Philadelphia 34-yard line. He even recovered his own fumble on the sack, grabbing the ball with the back of his legs as he fell to the ground — something of a reversal of his famed “butt fumble” while a member of the New York Jets on Thanksgiving 2012. The drive stalled, but not without a near­miraculous completion to ­Michael Floyd near the goal line after Sanchez was hit while throwing. Floyd — surrounded by two Eagles defenders — was unable to make the catch.

A 47-yard field goal made the score 14-13 at the end of what was easily the craziest half of the Redskins’ season.

After a scoreless third quarter, Philadelphia increased its lead early in the fourth after Carson Wentz finished an 11-play, 85-yard drive with a pass to Jordan Matthews, who dived into the end zone for a touchdown. A two-point conversion made it 22-13.

Three plays into the Redskins’ next possession, Sanchez threw a pass that was intercepted by ­Eagles linebacker Nathan Gerry, leading to a field goal that put Washington down 25-13. It was all too much for Sanchez, and the Redskins, to overcome on a crazy, crazy night.